Osteoclast Activating Factor (OAF) is a lymphokine which may be involved in stimulation of localized bone destruction in periodontal disease or other diseases where chronic accumulation of lymphoid cells accompanies bone destruction. The objectives of this study are to characterize OAF chemically and biologically, to develop specific immunologic assays for OAF in biological samples, and to examine the sources and regulation of OAF production. OAF will be isolated from mitogen-activated human lymphocytes, and purified by established procedures. The isolated active species will be chemically characterized as to their structure and composition. The isolated fractions will also be used to immunize animals against OAF. The effects of OAF on isolated bone and bone cells with be studied to determine the mechanisms of action of OAF in producing bone destruction. In order to furnish monospecific antibodies for OAF, hybrid cell lines will be established and propagated. The antibodies so obtained will be used to design immunoassay and immunocytochemical methods for detection and quantitation of OAF in tissue and serum. Finally, the cellular source of OAF will be examined by fractionation of human lymphocytes into subpopulations by density gradient and affinity separation techniques. These studies will allow determination of the role of OAF in vivo in pathologic circumstances.